Most vehicles today include air conditioning systems to provide for improved occupant comfort. While first introduced in the automotive world several decades ago, air conditioning systems have changed little. Thus the fundamental parts of the modern vehicle's air conditioning system are known and understood. These parts include the compressor, the condenser, the evaporator, the thermal expansion valve, and the drier or accumulator. In many ways the compressor is the heart of the vehicle's air conditioning system. The compressor pressurizes hot, gaseous refrigerant and forces it on to the condenser. The condenser, which is like a small radiator, cools the hot gases received from the compressor. As these gases cool, they become liquid in the condenser.
Liquid refrigerant leaves the condenser under high pressure and enters the drier or accumulator. The drier catches any liquid water that may inadvertently have entered the system. The liquid refrigerant, once cleared of any water, flows to the expansion valve which functions to remove pressure from the liquid refrigerant and literally allows it to expand. This reduction of pressure allows the liquid refrigerant to return to the vapor stage in the evaporator, the refrigerant's next stop.
The evaporator is also similar in shape and function to a small radiator. Typically the evaporator is fitted inside of the vehicle's passenger compartment in or around the instrument panel. The still-liquid refrigerant enters the evaporator under low pressure from the expansion valve. The liquid refrigerant vaporizes while absorbing heat from inside the car. Cold air is circulated within the passenger compartment by a fan that pushes air across the fins of the evaporator. Low pressure refrigerant, now in gaseous form, exits the evaporator and returns to the compressor where the cycle is repeated.
As fuel economy becomes an increasingly critical factor in the design of the automobile, many automobile manufacturers are equipping the engine with automatic start and stop technology. The start-stop technology enables the engine to be off while the vehicle is stopped, for example, at a stop light or in congested traffic. As some vehicles use mechanically belt-driven compressors to run the air conditioning system, the compressor will not function during the engine off time. Thus, an improvement in the air conditioning system components is required during the engine off time.